How an Air Conditioner Works
An air conditioning system works remarkably like a refrigerator. If fact, large walk-in refrigerators are essentially rooms with too much AC. The actual physics of the operation is that a compressor compresses a refrigerant into a high pressure, liquid state. This compressed refrigerant moves along a tube and then is allowed to expand into a larger space, which results in the refrigerant to going to a low pressure state. When a gas or liquid goes from a state of high pressure to low pressure, it cools down.
A cooling system works in the following way. A thermostat in the living space is set with a temperature that is the upper limit at which the home should be maintained. When the ambient temperature at the thermostat rises above the preset, a circuit closes (effectively a switch) allowing current to flow to the air conditioning controls and thus signalling it to begin cooling.
Central air conditioning systems have five major components, the refrigerant within a closed system of tubing, the compressor/condenser, the evaporator coils, blower and ductwork.
The compressor and condenser are typically housed together, it is the equipment that is installed outdoors. The compressor runs on electric current and compresses a refrigerant gas, converting it to a liquid under high pressure. Compressing a gas into a liquid has the opposite effect of the cooling process, it generates heat. This is where the condenser fan comes in, the refrigerant passes through a series of coils over which the fan blows in order to dissipate some of the heat. This is also why this equipment is outdoors, because you wouldn't want the heat dumped into the home you are trying to cool.
The refrigerant line then goes into the home and to the evaporator or cooling coils in the air handling system. An expansion valve allows the refrigerant to evaporate into a gas resulting in a significant temperature drop. The cooling coils are surrounded by thin metal fins like an automobile radiator. The fins maximize surface area to facilitate the most efficient exchange of heat. A blower is directed over the cooling coils and the air is cooled as it passes into the home's distribution ducts. The blower draws air from the interior of the home through an "air return" and then recirculates it through the ducts after first cooling the air.
As the cool air circulates throughout the home, the thermostat senses the temperature change and once it reaches the preset temperature, the switch opens and cuts power to the AC controls and the unit shuts down. The blower may operate for a short additional time to draw off the remaining cooling power of the chilled evaporator coils.